Il y a un an, nous n'utilisions pas cette application.

Il y a normally means “there is / there are” in the present:

• Il y a un problème. – There is a problem.

But with a time expression after it, il y a + time is a fixed structure that means “… ago.”

• Il y a un an – a year ago
• Il y a deux semaines – two weeks ago
• Il y a longtemps – a long time ago

Even though it refers to the past, il y a itself stays in the present tense in this expression. You don’t say ✗il y avait un an for “a year ago”; you keep il y a.

Yes. French is flexible with time expressions.

• Il y a un an, nous n'utilisions pas cette application.
• Nous n'utilisions pas cette application il y a un an.

Both are correct and natural.
Starting with the time expression can sound a bit more formal or emphatic; putting it at the end is very common in everyday speech.

Both an and année mean “year,” but they’re used differently:

• un an: neutral, used for counting or measuring time
  • Il y a un an. – A year ago.
  • J’ai 20 ans. – I am 20 years old.
• une année: emphasizes the duration, the content or “experience” of the year
  • Une année difficile – a difficult year
  • Toute l’année – all year long

In this sentence, we’re just measuring time, so un an is the normal choice.
You could hear Il y a une année in some styles, but it sounds marked or literary; Il y a un an is the standard everyday form.

It’s the difference between the imparfait and the passé composé:

• Imparfait (nous n'utilisions pas): describes ongoing, repeated, or habitual actions in the past.
  → “At that time, we weren’t in the habit of using it / we didn’t use it (as a general state).”

• Passé composé (nous n’avons pas utilisé): describes a completed action or single event.
  → “We didn’t use it (on that specific occasion).”

In Il y a un an, nous n'utilisions pas cette application, you’re talking about your general situation or habits a year ago, so the imparfait (utilisions) is appropriate.

Utilisions is imparfait, 1st person plural (nous) of utiliser.

To form the imparfait:

1. Take the nous form of the present tense:
   
   • nous utilisons
2. Remove -ons to get the stem:
   
   • utilis-
3. Add imparfait endings: -ais, -ais, -ait, -ions, -iez, -aient

So:

• je utilisais
• tu utilisais
• il/elle/on utilisait
• nous utilisions
• vous utilisiez
• ils/elles utilisaient

In your sentence, nous n'utilisions pas = we were not using / we didn’t use (as a habit).

This is elision: in French, ne becomes n’ before a verb that starts with a vowel sound (or a mute h).

• ne + utilisions → n'utilisions
• ne + avons → n'avons
• ne + aimons → n’aimons

This is compulsory in standard written French.
So you must write nous n'utilisions pas, not ✗nous ne utilisions pas.

The basic pattern in French is:

ne / n’ + verb + pas

In your sentence:

• nous – subject
• n’ – first part of the negation
• utilisions – verb
• pas – second part of the negation
• cette application – object

So you get:
Nous n’utilisions pas cette application.

Other examples:

• Je n’aime pas ça. – I don’t like that.
• Il ne parle pas français. – He doesn’t speak French.

In everyday speech, you’ll often hear changes:

1. Nous → on (very common in spoken French):

   • On n’utilisait pas cette application.

2. The ne / n’ is often dropped in informal spoken French:

   • On utilisait pas cette application.

So, in casual speech, many people would say:

• On utilisait pas cette application il y a un an.

But in writing or formal speech, you should keep ne / n’ and nous:

• Il y a un an, nous n’utilisions pas cette application.

Cette is the feminine singular form of the demonstrative adjective ce / cet / cette / ces:

• masculine singular before a consonant: ce
  • ce livre – this book
• masculine singular before a vowel or mute h: cet
  • cet ordinateur – this computer
• feminine singular: cette
  • cette application – this application
• plural (both genders): ces
  • ces applications – these applications

Application is feminine in French (une application), so you must use cette.

It’s a true friend here:

• une application (mobile / informatique) → a (mobile / software) app

However, application in French also has other meanings:

• l’application (d’une règle) – the application (of a rule)
• travailler avec application – to work diligently

In your sentence, with cette application, context usually makes it clear you mean a software app, especially in modern usage.

Approximate pronunciation (in IPA):

• nous n’utilisions pas → /nu ny.ti.li.zjɔ̃ pa/

Key points:

• nous → /nu/ (the final s is silent)
• n’ is just linking nous to utilisions; you hear /n/ joining to the vowel
• utilisions → /y.ti.li.zjɔ̃/
  • u → /y/ (like German ü)
  • final s is silent
  • -ions → /jɔ̃/ (a nasal sound, not pronounced as “ee-on”)
• pas → /pa/ (final s silent)

Spoken smoothly: [nu ny.ti.li.zjɔ̃ pa].

Yes, that’s perfectly correct:

• On n’utilisait pas cette application il y a un an.

Differences:

• on instead of nous:
  
  • on is very common in spoken French to mean “we.”
  • grammatically 3rd person singular, but in meaning it’s like English we.
• utilisait (imparfait, 3rd person singular) to match on, instead of utilisions (1st person plural for nous).

Meaning-wise, it’s the same: A year ago, we weren’t using this application.
In conversation, on n’utilisait pas… is more frequent; in more formal writing, nous n’utilisions pas… is safer.